1. Field of the Invention
The present invention relates to a communication technology, and in particular relates to a technology for realizing wireless communication between a master and a slave by frequency hopping spread spectrum.
2. Description of the Related Art
A game machine and a controller for the game machine operated by a user were generally connected via a cable, but a system for establishing a radio channel between the game machine and the controller has been proposed in recent years. By using a wireless controller, a user can enjoy a game in free posture.
The conventionally proposed system is on the precondition that a wireless communication device provided in the game machine is wireless connected to the wireless controller via one-to-one radio connection and a connection partner is uniquely decided. Thus, when a plurality of users use the wireless controllers, it is necessary to provide the dedicated communication devices, each of which is assigned to each wireless controller, in the game machine on a per-wireless controller basis. Accordingly, the user has to always prepare the wireless controller and the wireless communication device for connecting the wireless controller to the game machine in a pair, so that the use of the wireless controller is troublesome.
Frequency hopping spread spectrum is one of methods for realizing wireless communication. The frequency hopping spread spectrum is a spectrum spread communication method, in which a wide frequency band is divided into plural to set channels, and communication is carried out by switching the channels. In Japan, Bluetooth has 79 channels, which are set in a wide band of 2.4 GHz (2402 to 2480 MHz) every 1 MHz, and communication is carried out by switching the channels for 1600 times per second. When a transmission error occurs due to the collision of signals using the same frequency, the same data is retransmitted after hopping to another frequency.
As types of collision of a Bluetooth signal, collision with a signal on IEEE802.11b standards, collision with noise emitted from a microwave oven, collision with noise existing in the same frequency band as the Bluetooth and the like are supposed. In the case where a plurality of masters form piconets whose signal communication ranges are overlapped mutually, collision between the Bluetooth signals is also supposed. A hopping pattern is uniquely determined in each piconet, and hence the probability of the collision between the Bluetooth signals is not high. A Bluetooth communication system, however, is built upon a principle that communication quality is maintained by retransmitting the signal, even if the collision occurs. When there are two piconets in the same area, the probability of the occurrence of interference between the piconets is one in 79.
In the game system, when the wireless communication between the game machine and a plurality of wireless controllers is realized by the frequency hopping spread spectrum, it is necessary to consider latency, that is, delay in the transmission of data. Particularly, in a game much requiring real-time communication such as a fighting game, it is necessary to minimize communication delay. If the latency becomes worse, the game application cannot be operated well. Therefore, when the frequency hopping spread spectrum is used in communication environment which requires real-time communication, controlling the system to avoid an transmission error is better than controlling the system to retransmit data when the transmission error occurs due to the collision of signals.